The success of well treatment operations often depends on optimizing placement of fluids downhole. In the past, much interest has focused on methods for improving downhole placement of well treatment fluids used in acid stimulation and hydraulic fracturing operations. Both of these operations enhance the production of hydrocarbons within the formation.
During acid simulation, such as by matrix acidizing, acid or an acid-forming material is injected into the formation and the acid reacts with minerals in the formation. As a result, near-wellbore permeability is improved by the opening of channels or wormholes within the formation. Early attempts at optimizing the placement of acid downhole focused on injection of a simple acidic solution into the wellbore. However, where the treated formation contained sections with varying permeability, the injected acid typically acidized the zone within the formation which had the highest permeability and the highest degree of water saturation. A permeability contrast between areas of high permeability (treated areas) within the formation and areas of low permeability (untreated areas) resulted.
In order to provide uniform distribution of treatment fluid within a treated zone, chemical diverting fluids have been developed which increase flow resistance within the formation and thus allow for the flow of treatment fluids from the higher permeability and/or water saturated sections of the formation to the lower permeability or oil bearing sections.
In hydraulic fracturing, the stimulation fluid is injected into a wellbore under high pressure. Once the natural reservoir fracture gradient is exceeded, the fracturing fluid initiates a fracture in the formation that generally continues to grow during pumping. The treatment design generally requires the fluid to reach a maximum viscosity as it enters the fracture.
The viscosity of most stimulation fluids is generated using hydratable polymeric viscosifying agents. Crosslinking agents in these fluids increase the viscosity of the fluid and thus improve stimulation of the treated well. When used as a fracturing fluid, the gelled fluid can include a propping agent (i.e., proppant). The proppant remains in the produced fracture to prevent the complete closure of the fracture and to form a conductive channel extending from the wellbore into the formation being treated once the stimulation fluid is recovered.
Conventional crosslinking agents in stimulation fluids contain transition metals such as titanium, zirconium, aluminum, iron and antimony as well as mixtures thereof. Such conventional crosslinking agents include zirconium oxychloride, zirconium acetate, zirconium lactate, zirconium malate, zirconium citrate, titanium lactate, titanium malate, titanium citrate and the like. Other conventional crosslinkers include complexes of transition metal compounds such as zirconium/triethanolamine complexes.
While conventional crosslinking agents enable the requisite viscosity to be attained, they are not particularly environmentally friendly. A need exists for a crosslinking agent that would effectively increase the viscosity of the polymeric viscosifying agent, like a conventional crosslinking agent, but which is environmentally friendly having one or more of the attributes or capabilities described or shown in, or as may be apparent from, the other portions of this patent.